C Language Programming Library
Reference Guide

stdlib.h -
Memory Functions - free

Declaration:
void free(void *ptr);
Deallocates the memory previously allocated by a call to calloc, malloc, or
realloc. The argument ptr points to the space
that was previously allocated. If ptr points to a memory
block that was not allocated with calloc,
malloc, or realloc, or
is a space that has been deallocated, then the result is
undefined.